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Processing and Application of Ceramics 5 [4] (2011) 205–213

Structural and functional characterization of barium zirconium titanate / epoxy compositesFiliberto González Garcia1, César Renato Foschini2, Jose Arana Varela2, Elson Longo2, Francisco Moura1, Alexandre Zirpoli Simões3

1Federal University of Itajubá - Unifei - Campus Itabira, Rua São Paulo 377, Bairro Amazonas, P.O. Box 355, 35900-37, Itabira, Minas Gerais, Brazil2Chemistry Institute, Department of Chemistry-Physics, São Paulo State University, UNESP, 14800-900, Araraquara, São Paulo, Brazil3Engineering Faculty, São Paulo State University, UNESP, 12516-410, Guaratinguetá, São Paulo, BrazilReceived 1 September 2011; received in revised form 25 November 2011; accepted 13 December 2011

AbstractThe dielectric behavior of composite materials (barium zirconium titanate / epoxy system) was analyzed as a function of ceramic concentration. Structure and morphologic behavior of the composites was investigated by X-ray Diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), Raman spectroscopy, field emis-sion scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) analyses. Com-posites were prepared by mixing the components and pouring them into suitable moulds. It was demonstrated that the amount of inorganic phase affects the morphology of the presented composites. XRD revealed the presence of a single phase while Raman scattering confirmed structural transitions as a function of ceramic concentration. Changes in the ceramic concentration affected Raman modes and the distribution of particles along into epoxy matrix. Dielectric permittivity and dielectric losses were influenced by filler concentration.

Keywords: composite materials, oxides, polymers, electron diffraction

I. IntroductionIn recent years, there has been increased interest in

high dielectric constant flexible particulate compos-ites composed of a ferroelectric ceramic and polymer for high density energy storage and capacitor applica-tions [1]. Usually, the dielectric constant of such poly-mer based composites is rather low (about 50) because of the lower dielectric constant of the matrix (usually below 10) [1–5]. For instance, in BaTiO3/epoxy com-posites, although BaTiO3 has a relatively high dielec-tric constant (>1000), the effective dielectric constant (εeff) of the composite was as low as 50, even when the highest possible concentration of ceramics was incor-porated [2]. As the concentration of ceramics increas-es, unfortunately, the composite loses its flexibili-ty. A new generation of high dielectric materials such as barium zirconium titanate ceramics (BZT) can be

used in order to obtain composites with better per-formance. A number of theoretical studies and exper-imental observations have attempted to elucidate the remarkable (high) dielectric properties of BZT mate-rial. The interest in high strain piezoelectric materials increases for electromechanical transducers and vari-ous related applications [6]. Although the large fam-ily of lead-based perovskites and relaxors has shown great potential, lead-free compositions in these fami-lies will be of interest due to obvious future environ-mental concerns [7–12]. Modified Ba(Zr,Ti)O3 has shown systematic changes in dielectric, piezoelectric, and phase transition characteristics in the bulk ceramic and single crystal forms [13]. In the paraelectric state, just above Tc, BZT ceramics are attractive candidates for dynamic random access memories and tunable di-electric devices. In this study, Ba(Ti0.9Zr0.10)O3 powders (BZT) were employed to produce the composite ma-terial which was chosen because it has improved di-electric and ferroelectric properties [14]. Usually, the

* Corresponding author: tel: +55 12 31232765fax: +55 12 3123 2800, e-mail: [email protected]

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preparation of the BZT phase by chemical routes have attracted wide attention including the hydrolysis of metal alkoxides, the polymeric precursor method de-rived from the Pechini method [14,15], and the co-pre-cipitation of metal hydroxides and oxalates [16]. Al-though the chemical route facilitates the preparation of fine and homogeneous oxide powders with better reac-tivity and sinterability, its dielectric and ferroelectric properties are still very low. Alternatively, the solid-state reaction at 1200°C for 2 hours among the constit-uent BaCO3, TiO2 and, ZrO2 can result in single phase BZT powders. This method is important to efficiently control ceramic properties due to its strong influence on the grain size and dielectric and ferroelectric prop-erties by an oxygen interdiffusion, a chemical reaction, or structural defects in this particle size range. Mea-surements on dielectric permittivity as a function of temperature reveal anisotropic behaviour with a sharp phase transition which is indicative of a ferroelectric-relaxor behaviour [17–19].

Epoxy resins are being widely used in industrial ap-plications such as adhesives and matrices for composite materials. High performances must be achieved through the synthesis and processing of the materials; in partic-ular, good mechanical behaviour (stiffness and tough-ness) is expected. In previous studies, we evaluated the effects of an amine co-monomer on the thermal relax-ations and mechanical properties [20]. The system of bisphenol A (diglycidyl ether) with aliphatic epoxide amine hardeners such as triethylenetetramine is exten-sively studied and reported in the literature [21,22]. In this research, the dielectric performance of BZT/epoxy matrix composites was studied to analyze dielectric be-havior as a function of temperature and filler concentra-tion. The aim of this investigation in a near future is to develop high density energy storage and capacitor de-vices by a careful control of modifying filler properties and a proper powder treatment to maximize the powder loading and dielectric properties.

II. ExperimentalBisphenol A (diglycidyl ether) (DGEBA, DER 332)

(Aldrich Brazil S.A) with an epoxy equivalent weight of 174 g.eq-1 determined by acid titration [23], was used as an epoxy prepolymer in all the epoxy formulations studied. The epoxy resin was degassed in a vacuum oven for 2 h at 80°C. Triethylenetetramine (TETA, tech. 60 % from ACROS, Brazil S.A.), was used as a cur-ing agent, with an amine hydrogen equivalent weight of 26.8 g.eq-1, determined by potentiometric titration in aqueous media [24]. Table 1 displays the structure and characteristics of the epoxy system employed in this study. BaCO3 (Vetec, Brazil), ZrO2 (Inlab, Brazil) and TiO2 (Vetec, Brazil) (all analytical grade) were used. The curing agent and these compounds were used as re-ceived. Ba(Ti0.9Zr0.10)O3 (BZT) polycrystalline powders

were prepared by a mixed oxide method. All starting materials used were of analytical grade: BaCO3 (Vetec, 99.99%), ZrO2 (Inlab, 99.8%), TiO2 (Vetec, 99.8%). These materials were ball milled in an alcohol medi-um for 24 hours in a polyethylene bottle, using zirconia balls. Then, the slurry was dried and thermally treated at 900°C in an air atmosphere for 12 hours.

The resulting powders were mixed in isopropyl al-cohol by agitation at 6000 rpm for 5 minutes and the al-cohol was eliminated by heating at 65°C until a con-stant weight was achieved. The powder was thermally treated at 1200°C for 120 minutes using a heating and a cooling rate of 5 °C/min. The powder was milled using a planetary mill with ZrO2 balls (Fritsch, Pulverisette 7) for 90 minutes in isopropilic medium. The ceramic powders were added to the epoxy resin at different con-centration and then suitably blended using an ultrasonic mixer (Sonic vibra-cell 150 W) for 10 min. The speed during preparation of composition ceramic powder/ep-oxy resin was 2000 rpm. The epoxy resin was mixed with the powder using different concentrations: 5, 10 and 15 phr (5, 10 and 15 g of filler per 100 g of DGE-BA, respectively) before curing.

Epoxy composites were prepared by adding the cur-ing agent to the epoxy resin mixture using the stoichio-metric amount (epoxy ratio to amino-hydrogen e/a = 1). All formulations were mixed and degassed at room temperature under mechanical stirring for 15 min. The mixture was poured into polyethylene molds (cylindri-cal), cured in a forced air oven and cooled to room tem-perature. Each mixture was poured into glass moulds and cured at 100°C for 2 hours. The cure schedule was optimized by calorimetric studies to obtain fully cured networks. The glass transition temperature (Tg) of this system is 124°C [20]. XRD data were collected with a Rigaku Rint 2000 diffractometer under the follow-ing experimental condition: 50 kV, 150 mA, 20°≤ 2θ ≤ 80, ∆2θ = 0.02°, λCuKα monochromatized by a graph-ite crystal, divergence slit of 2 mm, reception slit of 0.6 mm, step time of 10 s. Raman measurements were per-formed using an ISAT 64000 triple monochromator. An optical microscope was employed to focus the 514.5 nm radiation from a Coherent Innova 99 Ar + laser on the sample and to collect the back-scattered radiation. The scattered light dispersed by the spectrometer was detect-ed by a charge-coupled device (CCD) detection system. FTIR spectra were recorded with a Bruker Equinox-55 instrument. Microstructural characterization was per-formed by FE-SEM (Supra 35-VP, Carl Zeiss, Germa-ny) and transmission electron microscopy (TEM, Jeol 3010 URP). Samples were painted with a silver paste for dielectric measurements which were performed us-ing a Hewlett Packard 4284A Impedance Analyser from 20 Hz to 1 MHz at room temperature. Dielectric per-mittivity and dielectric loss as a function of temperature were also measured.

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III. Results and discussionThe XRD pattern of the BZT/epoxy matrix com-

posites with different ceramic concentrations is shown in Fig. 1a. X-ray reflections show that a single phase with a pseudo-cubic perovskite structure was obtained. In all systems investigated, Bragg reflections peaks are indicative of a perovskite structure which is character-

ized mainly by a higher intense peak (hkl-110) at 2θ = 31° and no apparent peak splitting is identified. In-dependent of different filler amounts, Bragg reflections peaks reveal the formation of a stable solid solution be-tween the epoxy system and the BZT lattice since no extra peaks appeared in the XRD pattern. For compari-son, XRD pattern of pure BZT powder is shown in Fig. 1b. As can be seen, the room temperature XRD plot of Ba(Ti0.9Zr0.10)O3 powder crystallize into a single-phase perovskite structure. This is a clear indication that the addition of Zr is forming a stable solid solution with the BaTiO3 lattice.

Figure 2 shows the FT-IR spectrum of a BZT/ep-oxy matrix composite with different ceramic concen-trations. Regarding the ceramic structure, the main band characteristic of the oxygen-metal bond was ob-served in the region 450–640 cm-1 region. The vibra-tional mode located at around 1450 cm-1 is associated with an epoxy matrix related to methyl and methylene groups in the out-of-plane bending vibrational mode. Previous studies suggest that the absence of this band corresponds to a C=O relative to the powders which in-dicates that inorganic phases are free of carbonates [9]. This result is satisfactory from a technological point of view since of composite material properties depend on

Figure 1. X-ray data of: a) BZT/epoxy matrix composites with 5 (i), 10 (ii) and 15 phr (iii) and b) BZT powder

a) b)

Figure 2. FT-IR of BZT10/epoxy matrix composites with:a) 5, b) 10 and c) 15 phr

H N-(CH ) -NH-(CH ) -NH-(CH ) -NH2 2 2 2 2 2 2 2

CH CH2 CH O2 OCH CH2 CH2

CH3

C

CH3

O O

Table 1. Structure and characteristics of the epoxy system monomers

Monomers Formula SupplierM

[g.mol-1]F

Triethylenetetramine (TETA) ACROS 146 6

Diglycidyl etherof

bisphenol A (DGEBA)Dow Chemical

~ 348(174 g.eq-1)

2

M = molecular weight, F = functionality

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the powders properties used to prepare the two phase system. However, a vibrational band was observed that is associated with the deformation of O-H bonds near 3450 cm-1 which is attributed to stretching vibrations of composite O-H bonds. Regarding the epoxy ma-trix, the bands characteristic of this structure appear in the spectra [22]. The band around 3050 cm-1 is as-signed to C-H stretching vibrational sp2 bonds, and the bands around 2960, 2920 and 2880 cm-1 are associat-ed with C-H stretching vibrational sp3 bonds. The band at 2360 cm-1 indicates that the composite adsorbed CO2 from the atmosphere. Bands associated with the aro-matic ring appear around 1600, 1580, and 1500 cm-1. The band around 1020 cm-1 is associated with C-O-C ether groups while the band around 1250 cm-1 is associ-ated with C-N stretching vibration. The bands at 1360 and 1375 cm-1 can be assigned to methyl group bonds between the carbon aromatic ring and the band at 828 cm-1 which is assigned to the 1.4 substitution. The ab-sence of a band around 900 cm-1, which is associated to epoxy groups, indicates that the epoxy system has at-tained a high conversion. Although relative transmit-tance values increase with an increase in the amount of filler, no extra bands appeared in the spectrum which indicates the formation of a stable solid solution be-tween the epoxy matrix and the BZT lattice. The in-crease in epoxy peaks intensity as the ceramic content increases indicates that the mixing process of filler and epoxy resin was carried out for only few minutes and resulted in a non-homogeneous oxide distribution in the epoxy matrix.

Room temperature Raman spectra are displayed in Fig. 3. Because of the random grain orientations in the powders evidenced by SEM and not shown in the text, the directions of the phonon wave vectors are random-ly distributed from one grain to another with respect to the crystallographic axes. The evolution of Raman spectra with ceramic concentration shows some inter-esting changes. As observed, at increased ceramic con-centration, the Raman line at 123 cm-1 is absent. Tak-ing the mass ratio Zr/Ti = 1.9 into consideration this mode frequency is expected to be about 129 cm-1 for Zr replacing Ti sites which will be further reduced by an increase in the ionic radius [R (Ti4+) = 0.0745 nm, R (Zr4+) = 0.086 nm]. The additional mode could there-fore be associated with a normal mode involving Zr at-oms. Since this mode disappears with a more concen-trated amount of ceramic, it may be considered as an indication of short range structural disordering. These observations could not be observed in the X-ray studies due to the different coherence length and time scale in-volved in the process. The modes further split into lon-gitudinal (LO) and transverse (TO) components due to long electrostatic forces associated with lattice ionic-ity, which are caused by Ba2+ ions in BaTiO3 such as reported for the Ba(Zr0.10Ti0.90)O3 lattice [25,26]. The

spectrum shows the stretching mode of A1(TO1) and A1(TO3) at around 193 and 517 cm-1, according to the references [27,28]. The E1(TO1) and E1(TO2) modes that are associated with the tetragonal-cubic phase transition were observed at 116 and 301 cm-1, where-as the A1(LO3) mode was found at 720 cm-1, with zir-conium (Zr) substituted at the titanium (Ti) sites. How-ever, the coupling between the sharp A1(TO1) and broad A1(TO2) modes reduces as the intensity of the A1(TO2) mode decreases [29,30].

A SEM analysis of a BZT/epoxy matrix compos-ite is shown in Fig. 4a-c. For comparison, SEM fig-ure of epoxy matrix was presented. An increase in the agglomerates size was observed as the amount of ce-ramic powder increases. The agglomerates are round-ed in form which is typical for the mixed oxide meth-od. Regions without filler or trails of micro-porosity are observed as are particles with a low size and a rel-ative fine size distribution. In all samples, particle ag-glomeration results from a non-homogeneous disper-sion of particles during the mixing step. It is clear that mixing in a mortar and pestle generates a simple mix-ture where the components could be identified sepa-rately. Although particle agglomeration exists, our data reveal that the inorganic phase and epoxy matrix are homogeneously distributed in the particle. An intimate mixing of the barium zirconium titanate and the epoxy matrix yields a composite which suggests that the com-posite actually consists of fine agglomerates composed of an oxide on the epoxy matrix. The BZT/epoxy ma-trix composite with 10 phr consists of more homoge-neous surface morphology (Fig. 4b). SEM micrograph of epoxy resin reveals a continuous phase with smooth areas indicating larger solubility of the modifiers and a complete polymerization rate.

TEM analyses of the BZT/epoxy matrix compos-ite with 10 phr is illustrated in Fig. 5. A closer look at the darker part (bottom left-A) reveals that it is actual-ly an agglomerate composed of a large number of par-

Figure 3. Raman analyses of BZT10/epoxy matrix composites with (a) 5, (b) 10 and (c) 15 phr

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ticles while white regions are believed to be the epoxy matrix (top-B). The inorganic phase and the epoxy ma-trix can be clearly distinguished. The darker part corre-sponds to barium zirconium titanate as confirmed by a further magnification which indicates randomly grown crystallites. The epoxy matrix is visible at the bottom (center) and the top of the image while part of a struc-tured oxide is located at the left. It is clear that an inti-mate mixing of the barium zirconium titanate and the epoxy matrix yields a composite (center-C). The mixing of an inorganic phase and epoxy system is desirable to achieve good end-use properties and a better composite efficiency. It is possible that the composites may also provide better pathways for ion diffusion and lower ion-ic resistance during the charge-discharge process which is useful for dynamic random access memory (DRAM) applications.

The temperature dependence of dielectric permit-tivity is shown in Fig. 6a. The dielectric permittivity

Figure 5. TEM micrograph of BZT10/epoxy matrixcomposite with 10 phr evidencing (A) agglomerate of

particles, (B) epoxy matrix and (C) composite

Figure 4. SEM micrographs of BZT10/epoxy matrix composites with (a) 5, (b) 10, (c) 15 phr and (d) SEM micrography of pure epoxy matrix

a)

c)

b)

d)

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measured at 10 kHz are 36, 66 and 28 while the dielec-tric losses are 0.13, 0.30 and 0.22 for 5, 10 and 15 phr, respectively. For a 10 phr composite, the phase transi-tion is observed at 66°C, and its maximum dielectric permittivity (εm) reaches 66. In this sample, a structural phase transition occurs which corresponds to the tran-sition of a paraelectric (cubic) to ferroelectric (tetrag-onal) phase (at Tc). The dielectric permittivity increas-es gradually with an increase in temperature up to the transition temperature (Tc) or Curie point and then de-creases. Also, the maximum dielectric permittivity (εm) and the corresponding maximum temperature, (Tm), depend on the ferroelectric ceramic concentration. The magnitude of the dielectric permittivity decreas-es in this case, and the Curie temperature shifts toward a lower temperature which indicates that dielectric po-larization is a relaxation type in nature. The region around the dielectric peak is broadened due to a disor-der in the cations arrangement in one or more crystal-lographic sites of the structure [31,32]. The reduction

of dielectric permittivity with 15 phr indicates that fill-er agglomerates are deleterious for the improvement of composite properties. For the epoxy matrix, the rela-tive dielectric permittivity remains around 5.7 and the dielectric loss is 0.018 at 25°C [33]. Figure 6b shows the temperature dependence of dielectric loss deter-mined at 10 KHz. The dielectric loss is almost tempera-ture independent, although it also presents a very small peak just below Tc. At lower temperatures, a small tem-perature dependence of dielectric loss was observed with stabilization at elevated temperatures. The pos-sible formation of metal vacancies may result in a re-duced dielectric loss at elevated temperatures and re-flects that good insulation resistance was maintained at high temperatures which is important in the develop-ment of high density energy storage and capacitor de-vices. In addition, the dielectric loss was much lower than the dielectric loss of pure BZT ceramics reported in our previous work [34] which is attributed to the de-crease in space charge density as the epoxy resin is in-

Figure 6. Temperature dependence of dielectric permittivity (a) and dielectric loss (b) at 10 KHz for BZT10/epoxy matrix composites with 5, 10 and 15 phr

Figure 7. Temperature dependence of dielectric permittivity (a) and dielectric loss (b) at 10 kHz for triethylenetetramine

a)

a)

b)

b)

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corporated in the BZT lattice. The higher value of di-electric loss at elevated temperatures may be due to the transport of ions with higher thermal energy. The sharp increase in dielectric loss may be due to the scatter-ing of thermally activated charge carriers and the pres-ence of defects. At higher temperatures the conductiv-ity begins to dominate, which in turn is responsible for the rise in dielectric loss that is associated with con-duction loss. Also, at a high temperature (paraelectric phase) the contribution of ferroelectric domain walls to dielectric loss decreases. Chahal et al. [33] reported di-electric permittivity of 39 and 22 for 55 vol% ceram-ic/polyacrylonitrile and for the 50% ceramic/polynor-bornene composites, respectively. Bhattacharya et al. [35] reported dielectric permittivity of 9 and 34 for two kinds of PWB- compatible composites at a filler load-ing of 21 and 46%, respectively. The dielectric permit-tivity of 66 with a filler loading of 10 phr in this study thus compares favorably with these literature data. The changes which occur in the dielectric loss are due to extrinsic resonance behaviour which may be caused by defects (vacancy, movable ion, leaky grain boundary, etc.) that developed in the structure of the bulk materi-al with donor dopants [36–46].

The temperature dependence of dielectric permit-tivity is shown in Fig. 7a for the triethylenetetramine. The dielectric permittivity measured at 10 kHz is 14 while the dielectric losses are 0.016, respectively. The dielectric permittivity increases gradually with an increase in temperature up to the transition tem-perature (Tc) or Curie point and then decreases. The rise in dielectric loss at higher temperatures is associ-ated with the conductivity which in turn is responsi-ble for loss values. Changes in the permittivity values as a function of temperature are attributed to dielec-tric relaxations which are more pronounced at high-er temperatures due to the micro-Brownian motion of the whole chain (segmental movement). Nevertheless, these changes are also affected by the interfacial po-larization process known as Maxwell-Wagner-Sillar, which exists in heterogeneous dielectric materials and is produced by the traveling of charge carriers [47]. Relaxations peaks were influenced by the interfacial polarization effect which generates electric charge ac-cumulation around the polymeric chain and the dis-placement of charges around it [48].

IV. ConclusionsSingle phase BZT composite materials were ob-

tained using a mixed oxide method. The structure and morphologic behavior of an epoxy system/barium zir-conium titanate powder was analyzed as a function of ceramic concentration that revealed a perovskite struc-ture with rounded agglomerates which is typical for the mixed oxide method. Raman spectroscopy indicat-ed a change in the crystal structure with an increase in

the ceramic concentration which indicated short-range structural disordering. TEM analyses confirmed an in-timate mixing of the barium zirconium titanate and the epoxy matrix to produce a composite. The inorganic phase consists of randomly grown crystallites while the epoxy matrix is viewed as the most of structured composite. Low porosity and better homogeneous size distribution is evident for the BZT/epoxy matrix com-posite with 10 phr. The dielectric permittivity was in-fluenced by the filler concentration volume because particle distribution is the most important parameter which affects composite permittivity values. To obtain the best dielectric properties of ceramic BZT/epoxy composites, proper powder treatment is required to maximize the powder loading and dielectric properties by carefully controlling the particle size, phase con-tent and elimination of constraint forces from neigh-boring grains.

Acknowledgements: The authors gratefully acknowl-edge to the financial support of the Brazilian agencies FAPESP, CNPq, and CAPES.

ReferencesY.J. Li, M. Xu, Z.M. Dhang, “Dielectric behavior of a 1. metal-polymer composite with low percolation thresh-old”, Appl. Phys. Lett., 89 (2006) 072902-072904. D-H. Kuo, C-C. Chang, T-Y. Su, W-K. Wang, B-Y. 2. Lin, “Dielectric behaviours of multi doped BaTiO3/epoxy composites”, J. Eur. Ceram. Soc., 21 (2001) 1171–1177.R. Gregório, J.M. Cestari, F.E. Bernardino, “Dielectric 3. behaviour of thin films of β-PVDF/PZT and β-PVDF/BaTiO3 composites”, J. Mater. Sci., 11 (1996) 2925–2930.H.L.W. Chan, W.K. Chan, Y. Zhang, C.L. Choy, “Py-4. roelectric and piezoelectric properties of lead titana-te/polyvinylidene fluoride-trifluoroethylene 0-3 com-posites”, IEEE Trans. Dielectr. Electr. Insul., 4 (1998) 505–512.C.J. Dias, D.K. Das-Gupta, “Inorganic ceramic/poly-5. mer ferroelectric composite electrets”, Dielectr. Elec-tr. Insul., 5 (1996) 706–734.Z.Yu, R. Yu, A.S. Bhalla, “Dielectric behavior of 6. Ba(Ti1-xZrx)O3 single crystals”, J. Appl. Phys., 88 (2000) 410–415.Z. Yu, C. Ang, R. Guo, A.S. Bhalla, “Dielectric prop-7. erties and high tunability of Ba(Ti0.7Zr0.3)O3 ceramics under dc electric field”, Appl. Phys. Lett., 81 (2002) 1285–1287.A. Dixit, S.B. Majumder, R.S. Katiyar, “Relaxor be-8. havior in sol-gel-derived BaZr(0.40)Ti(0.60)O3 thin films”, Appl. Phys. Lett., 82 (2003) 2679–2681.P.S. Dobal, R.S. Katiyar, “Studies on ferroelectric pe-9. rovskites and Bi-layered compounds using micro-Ra-man spectroscopy”, J. Raman. Spectrosc., 33 (2002) 405–423.

212


A. Dixit, S.B. Majumder, A. Savvinov, R.S. Katiyar, 10. R. Guo, A.S. Bhalla, “Investigations on the sol-gel-derived barium zirconium titanate thin films”, Mater. Lett., 56 (2002) 933–940.D.S. Paik, S.E. Park, S. Wada, S.F. Liu, T.R. Shrout, 11. “E-field induced phase transition<001>-oriented rhombohedral 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 crys-tals”, J. Appl. Phys., 85 (1999) 1080–1083.D. Hennings, H. Schell, “Diffuse ferroelectric phase-12. transitions in Ba(Diffuse ferroelectric phase-transi-tions in Ba(Ti1-yZry)O3 ceramics”, J. Am. Ceram. Soc., 65 (1982) 539–544.Mc Quarrie, F.W. Behnke. “Structural and dielectric 13. studies in the system (Ba, Ca) (Ti, Zr)O3”, J. Am. Ce-ram. Soc., 37 (1954) 539–543.F. Moura14. , A.Z. Simões, L.S. Cavalcante, M.A. Zaghe-te, J.A. Varela, “Influence of tungsten dopant on sinte-ring and Curie temperatures of Ba(Zr0.10Ti0.90)O3 cera-mics”, Ferroelectrics, 367 (2008) 120–130.M.P. Pechini, “Method of preparing lead and alkaline 15. earth titanates and niobates and coating method using the same to form a capacitor”, US Patent 3330697, 11 July (1967).M.A. Zaghete, C.O. Paiva-Santos, J.A. Varela, E. Lon-16. go, Y.P. Mascarenhas, “Phase characterization of lead zirconate titanate obtained from organic solutions of citrates”, J. Am. Ceram. Soc., 75 (1992) 2088–2093.J. Choy, Y. Han, S. Kim, “Oxalate coprecipitation 17. route to the piezoelectric. Pb(Zr, Ti)O3 oxide”, J. Mat-er. Chem., 7 (1997) 1807–1813.F. Moura, A.Z. Simões, E.C. Aguiar, I.C. Nogueira, 18. M.A. Zaghete, J.A. Varela, E. Longo, “Dielectric in-vestigations of vanadium modified barium titanate zir-conate ceramics obtained from mixed oxide method”, J. Alloys Compds., 479 (2009). 280–283.F. Moura, A.Z. Simões, B.D. Stojanovic, M.A. Zaghe-19. te, J.A. Varela, E. Longo, “Dielectric and ferroelect-ric characteristics of barium zirconate titanate cera-mics prepared from mixed oxide method”, J. Alloys. Comp., 462 (2008) 129–134.F. González Garcia, M.E. Leyva, M.C. Oliveira, 20. A.A.A. Queiroz, A.Z. Simões, “Influence of chemical structure of hardener on mechanical and adhesive pro-perties of epoxy polymers”, J. Appl. Polym. Sci., 117 (2010) 2213–2219.C.A. May, 21. Epoxy Resins. Chemistry and Technology, New York, Marcel Dekker. 1988.H. Lee, K. Neville, 22. Handbook of Epoxy Resins, New York, McGraw-Hill & Inc. 1967. F. González Garcia, P.M. Da Silva, B.G. Soares, 23. J. Rieumont, “Combined analytical techniques for the determination of the amine hydrogen equivalent weight in aliphatic amine epoxide hardeners”, Polym. Test., 26 (2007) 95–101.A. Chaves, R.S. Katiyar, S.P.S. Porto, “Coupled 24. modes with A1 symmetry in tetragonal BaTiO3”, Phys. Rev. B., 10 (1974) 3522–3533.

P.S. Dobal, A. Dixit, R.S. Katiyar, Z. Yu, R. Guo, 25. A.S. Bhalla, “Micro-Raman scattering and dielect-ric investigations of phase transition behavior in the BaTiO3–BaZrO3 system”, J. Appl. Phys., 89 (2001) 8085–8091.J. Kreisel, P. Bouvier, M. Maglione, B. Dkhil, A. Si-26. mon, “High-pressure Raman investigation of the Pb-free relaxor BaTi0.65Zr0.35O3”, Phys. Rev. B., 69 (2004) 092104–092107.B.D. Begg, K.S. Finnie, E.R. Vance, “Raman study 27. of the relationship between room-temperature tetrago-nality and the curie point of barium titanate”, J. Am. Ceram. Soc., 79 (1996) 2666–2672.P.S. Dobal, A. Dixit, R.S. Katiyar, Z. Yu, R. Guo, A.S. 28. Bhalla, “Micro-Raman scattering in Nb2O5-TiO2 cera-mics”, J. Raman. Spectrosc., 33 (2002) 121–124.A. Dixit, S.B. Majumder, P.S. Dobal, R.S. Katiyar, 29. A.S. Bhalla, “Phase transition studies of sol-gel depo-sited barium zirconate titinate thin films”, Thin Solid Films, 447 (2004) 284–287.L. Ramajo, M. Reboredo, M. Castro, “Dielectric re-30. sponse and relaxation phenomena in composites of epoxy resin with BaTiO3 particles”, Composites Part A., 36 (2005) 1267–1274.M.E. Lines, A.M. Glasss, 31. Principles and applications of ferroelectrics and related materials, Oxford Uni-versity Press, Oxford 1977.Y. Wu, S.J. Limmer, T.P. Chou, C. Nguyen, C. Guoz-32. hong, “Influence of tungsten doping on dielectric pro-perties of strontium bismuth niobate ferroelectric ce-ramics”, J. Mater. Sci. Lett., 21 (2002) 947–949.P. Chahal, R.R. Tummala, “A novel integrated de-33. coupling capacitor for MCM-L technology”, IEEE Trans. Comp. Packag. Manufact. Technol., B 21 (1998) 184–193. A.Z. Simões, C.S. Riccardi, A.H.M. Gonzalez, A. 34. Ries, E. Longo, J.A. Varela, “Piezoelectric proper-ties of Bi4Ti3O12 thin films annealed in different atmo-spheres”, Mater. Res. Bull., 42 (2007) 967–974.S. Bhattacharya, R.R. Tummala, P. Chahal, G. White, 35. pp. 68–70 in International Symposium on Advanced Packaging Materials, Atlanta, USA, 1997.A.Z. Simões, M.P. Cruz, A. Ries, E. Longo, J.A. Vare-36. la, R. Ramesh, “Ferroelectric and piezoelectric prop-erties of bismuth titanate thin films grown on differ-ent bottom electrodes by soft chemical solution and microwave annealing”, Mater. Res. Bull., 42 (2007) 975–981.A.Z. Simões, E.C. Aguiar, A. Ries, E. Longo, J.A. Va-37. rela, “Niobium doped Bi4Ti3O12 ceramics obtained by the polymeric precursor method”, Mater. Lett., 61 [2] 2007, 588–591.L.S. Cavalcante, A.Z. Simões, L.P.S. Santos, 38. M.R.M.C. Santos, E. Longo, J.A. Varela, “Dielectric properties of Ca(Zr0.05Ti0.95)O3 thin films prepared by chemical solution deposition”, J. Solid State Chem., 179 (2006) 3739–3743.

213


A.Z. Simões, M.A. Ramírez, B.D. Stojanovic, E. Lon-39. go, J.A. Varela, “The effect of microwave annealing on the electrical characteristics of lanthanum doped bis-muth titanate films obtained by the polymeric precur-sor method”, Appl. Surf. Sci., 252 (2006) 8471–8475.A.Z. Simões, S. Cava, L.S. Cavalcante, M. Cilense, E. 40. Longo, J.A. Varela, “Ferroelectric and dielectric prop-erties of Ba0.5Sr0.5(Ti0.80Sn0.20)O3 thin films grown by the soft chemical method”, J. Solid State Chem., 179 (2006) 2972–2976.A.Z. Simões, M.A. Ramírez, E. Longo, J.A. Varela, 41. “Leakage current behavior of Bi3.25La0.75Ti3O12 ferro-electric thin films deposited on different bottom elec-trodes”, Mater. Chem. Phys., 107 (2008) 72–76.L.S. Cavalcante, A.Z. Simões, M.O. Orlandi, M.R.M. 42. C. Santos, J.A. Varela, E. Longo, “Dependence of an-nealing time on structural and morphological proper-ties of Ca(Zr0.05Ti0.95)O3 thin films”, J. Alloys Compd., 453 (2008) 386–391. D.P. Volanti, D. Keyson, L.S. Cavalcante, A.Z. Simões, 43. M.R. Joya, E. Longo, J.A. Varela, P.S. Pizani, A.G. Souza, “Synthesis and characterization of CuO flower-nanostructure processing by a domestic hydrothermal microwave”, J. Alloys Compd., 459 (2008) 537–542.

A.Z. Simões, M.A. Ramirez, C.S. Riccardi, E. Longo, 44. J.A. Varela, “Effect of the microwave oven on struc-tural, morphological and electrical properties of Sr-Bi4Ti4O15 thin films grown on Pt/Ti/SiO2 /Si substra-tes by a soft chemical method”, Mater. Character., 59 (2008) 675–680. D. Keyson, D.P. Volanti, L.S. Cavalcante, A.Z. 45. Simões, J.A. Varela, E. Longo, “CuO urchin-nano-structures synthesized from a domestic hydrother-mal microwave method”, Mater. Res. Bull., 43 (2008) 771–775.M. Zhang, Z. Jin, J. Zhang, X. Gou, J. Yang, X. Wang, 46. Z. Zhang, “Effect of annealing temperature on mor-phology, structure, and photocatalytic behavior of na-notubed H2Ti2O4(OH)2”, J. Mol. Catal. A: Chem., 217 (2004) 203–210.G. Psarras, E. Manolakaki, G.M. Tsangaris, “Electri-47. cal relaxations in polymeric particulate composites of epoxy resin and metal particles”, Composites Part A., 33 (2002) 375–384.G. Tsangaris, N. Kouloumbi, S. Kyvelidis, “Interfa-48. cial relaxation phenomena in particulate composites of epoxy resin with copper or iron particles”, Mater. Chem. Phys., 44 (1996) 245–250.

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